A conventional mechanism for reducing fuel pressure pulsation is configured to hold a metal damper which is formed by joining two metal diaphragms and sealing gas inside the two metal diaphragms, between a damper chamber provided in a pump main body and a cover fitted onto the main body, and is housed in the damper chamber formed in a low pressure fuel passage leading to a pressure chamber of a high pressure fuel supply pump.
More specifically, two metal diaphragms are welded at their outer peripheries, have a disk-shaped convex portion with gas sealed in a center, and include an annular flat plate portion in which the two metal diaphragms are superimposed on each other, between the weld portion at the outer periphery and the disk-shaped convex portion. There are known a damper mechanism in which both outer surfaces of the flat plate portion are held by thick portions provided at a cover and a main body, or a damper mechanism in which elastic members are sandwiched between the cover and the annular flat plate portion and between the main body and the annular flat portion to hold them.
Further, there are known high pressure fuel supply pumps including such mechanisms for reducing fuel pressure pulsation (see JPA-2004-138071, JP-A-2006-521487, JP-A-2003-254191 and JP-A-2005-42554).    [Patent Document 1] JP-A-2004-138071    [Patent Document 2] JP-A-2006-521487    [Patent Document 3] JP-A-2003-254191    [Patent Document 4] JP-A-2005-42554